Viscosity of diluent and sensory level of subarachnoid anaesthesia achieved with tetracaine.
OBJECTIVE
Our objective was to evaluate the effect of viscosity in determining the cephalad spread of tetracaine administered by the subarachnoid route.


METHODS
We studied 42 patients that were randomly assigned to receive subarachnoid anaesthesia for arthroscope of the knee. They received 8 mg tetracaine dissolved in either glucose 10%, sodium chloride (NaCl) 5%, glucose 5%, or NaCl 2.5%. The specific gravity and viscosity of each solvent was also measured. Cephalad spread was defined as the level of sensory block achieved.


RESULTS
The specific gravity of the glucose 5% and the NaCl 2.5% solutions were similar (1.0197 +/- 0.0001 vs 1.0177 +/- 0.0001 (mean +/- SD)). That was also true for the more concentrated pair of solutions (1.0385 +/- 0.0001 for glucose 10% vs 1.0353 +/- 0.0003 in NaCl 5%). However, the viscosities of the 10% and 5% solutions of glucose (0.01178 +/- 0.0002 and 0.01020 +/- 0.0002 (g.cm-1.sec-1)) were higher (P < 0.05) than that of the other two solutions, being 0.00955 +/- 0.0001 for NaCl 5% and 0.00934 +/- 0.0002 for NaCl 2.5%. The median maximal extent of sensory block achieved was significantly higher (P < 0.05) with a solution of tetracaine in glucose 10% injected into the subarachnoid space at the L3-4 interspace than that observed in the two groups administered tetracaine in NaCl. The level of sensory block 30 min after the injection of anaesthetic was; T3 [T1-6] (median [range]) with glucose 10%, T6 [T4-10] with NaCl 5%, T5 [T2-11] with glucose 5%, and T5.5 [T2-11] with NaCl 2.5%.


CONCLUSIONS
Viscosity was shown to be one of determinants of the clinical extent of spread of a subarachnoid anaesthetic such as tetracaine.
Okutomi
T
T
Department of Anesthesiology, Kitasato University School of Medicine, Japan.
Nemoto
M
M
Mishiba
E
E
Goto
F
F
D000293:Adolescent; D000328:Adult; D000775:Anesthesia, Spinal; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000737:chemistry; D001182:Arthroscopy; D005069:Evaluation Studies as Topic; D005260:Female; D005947:Glucose / Q000008:administration & dosage / Q000737:chemistry; D006801:Humans; D007719:Knee Joint / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009407:Nerve Block; D012677:Sensation / Q000187:drug effects*; D012965:Sodium Chloride / Q000008:administration & dosage / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013046:Specific Gravity; D013129:Spinal Puncture; D013346:Subarachnoid Space; D013748:Tetracaine / Q000008:administration & dosage* / Q000737:chemistry; D014783:Viscosity
D000779:Anesthetics, Local; D012997:Solvents; D013748:Tetracaine; D012965:Sodium Chloride; D005947:Glucose